1. Field of the Invention
This invention relates to a method of forming images through heat development.
2. Discussion of the Background
Photographic processes using silver halides have been most widely used because of their improved photographic properties of sensitivity and gradation control over other photographic processes including electrophotography and diazo process. An advanced technique which can more conveniently and rapidly produce images through a dry treatment as by heating was recently developed as a substitute for a conventional wet treatment using developing solution in processes for forming images in a photosensitive material based on silver halide.
A number of methods have been proposed for producing color images through a dry process. A process for forming a color image through coupling of an oxidant of a developing agent with a coupler is described in several patents, for example, U.S. Pat. No. 3,531,286 disclosing p-phenylenediamine reducing agents combined with phenolic or active methylene couplers; U.S. Pat. No. 3,761,270 disclosing p-aminophenol reducing agents; Belgian Patent No. 802,519 and Research Disclosure, September 1975, pages 31-32 disclosing sulfonamidophenol reducing agents; and U.S. Pat. No. 4,021,240 disclosing sulfonamidophenol reducing agents combined with four equivalent couplers.
Research Disclosure, May 1978, pages 54-58, RD-16966 describes a process of forming an image by incorporating a nitrogen-containing heterocyclic group into a dye to form a silver salt and effecting heat development to release the dye.
A process for forming a positive color image by heat-sensitive silver dye bleaching process is also well known. Useful dyes and bleaching processes are disclosed in, for example, Research Disclosure, April 1976, pages 30-32, RD-4433; ibid, December 1976, pages 14-15, RD-15227; and U.S. Pat. No. 4,235,957.
A process for forming a color image using a leuco dye is described in, for example, U.S. Pat. Nos. 3,985,565 and 4,022,617.
These color image forming processes, however, have the drawbacks that it takes a relatively long time to complete development and there result heavily fogged images with a relatively low density.
To eliminate these drawbacks, Japanese Patent Application Kokai No. 58-79247 discloses a heat-developable photosensitive material comprising a dye-providing substance which reacts with an oxidant of a reducing agent to release a hydrophilic dye. The photosensitive material used in an image forming method of this type contains a surfactant for the purposes of preventing interlaminar color mixing, fogging, development irregularities associated with the temperature of heat development or the amount of water applied, image irregularities caused by paper making irregularities in a paper support of dye-fixing material, and other defects.
Japanese Patent Application Kokai Nos. 59-57231 and 60-79709, inter alia, disclose polyalkylene oxides, for example, ##STR1## which are found to substantially prevent interlaminar color mixing and fogging.
The surfactant is generally added to a layer, typically an emulsion layer which contains an emulsion (typically oil-protected emulsion) of a dye substance such as dyes and dye-providing substances. Agglomerates often form in these emulsions. It is presumed that since the surfactant breaks the emulsion, the dye substance precipitates to form agglomerates. This phenomenon is outstanding with emulsions of dye substances having a low solubility in oil.
If the surfactant is added to an emulsion-free layer such as intermediate and protective layers to alleviate demulsification, the interface between a surfactant-containing layer and an emulsion-containing layer becomes rough, leaving a problem. This phonomenon becomes outstanding particularly when multiple layers are coated at the same time. The cause is not clearly understood. When the surfactant is added to an intermediate layer, for example, the surfactant starts diffusing into the emulsion-containing layer, for example, through the as-coated surface before the intermediate layer being coated is bonded to the support. Then the viscosity of the emulsion-containing layer is extremely reduced to disorder the interface between the intermediate layer and the emulsion layer. Such a viscosity drop occurs in the emulsion layer probably because an increase of viscosity achieved by the emulsion is offset by demulsification.
It is undesirable that the surfactant which would create agglomerates in an emulsion-containing layer is added to even an emulsion-free layer.
The conventional surfactants are less suitable in the preparation of photosensitive material for the above reason. The demulsifying nature of surfactant may be somewhat alleviated in the preparation of photosensitive material by reducing the amount of surfactant added or adding divided parts of the surfactant to plural layers rather than adding the surfactant to a single layer, but at the sacrifice of intermediate color mixing prevention.
Further, the conventional surfactants are also insufficient in photographic properties including development irregularities and paper irregularities. Image irregularities resulting from paper irregularities become serious when a substantially water-insoluble metal compound is used in combination with a complexing compound capable of complexing with a metal ion of the metal compound as described in copending U.S. Ser. No. 890,442 based on Japanese Patent Application No. 60-169585. When such a base generating method is used, paper irregularities tend to incur irregularities in film thickness and pH, eventually leading to image irregularities.
There is a need for improvements in these problems.